This invention relates to an electrostriction transducer which makes use of the longitudinal electrostriction effect known in the art.
Electrostriction transducers are widely used as electrically controllable mechanical driving power sources in a printing head of an impact printer besides in relays, switches, and positioning apparatus. As will later be described more in detail, an electrostriction transducer usually comprises a rectangular pile or heap in which electrostriction layers are stacked on one another axially of the pile with internal electrodes interposed. Although called "internal," the electrodes are spread also on axial ends of the pile. In an electrostriction transducer of the type described, a pair of protection or dummy layers are fixed to both ends of the pile for the purpose which will become clear as the description proceeds. Each protection layer may be made of an electrostriction material of which the electrostriction layers are manufactured. The protection layer is not different in this respect from the electrostriction layers. the protection layer is, however, in contact with only one internal electrode that is spread on each end of the pile.
It is therefore possible at any rate to understand that an electrostriction transducer of the type being considered, comprises a column of an electrostriction material having an axis and a pair of axial ends with internal electrodes disposed in the column to divide the column into a pile of electrostriction layers stacked on one another along the axis and a protection layer positioned between the pile and each of the axial ends. The electrostriction transducer further comprises a pair of external electrodes for supplying a voltage to the internal electrodes to produce electric fields in the electrostriction layers parallel to the axis and to produce an axial elongation of the pile.
As will also be described in the following, the electrostriction transducer is subjected to breakage or like mechanical damages when repeatedly put into operation a number of times. In other words, conventional electrostriction transducers of the type described, have been of a short life and of a low reliability. It has now been confirmed that the liability to the mechanical damages results from concentration of shearing stresses at an interface between the pile and each protection layer.